The present invention relates to improved rotary compressors and, more particularly to compressors of the Root's type which are suitable for efficient operation at relatively high compression ratios.
The conventional lobe or Root's-type blower or compressor has been traditionally employed in high capacity-low pressure applications. At high compression ratios, over two for example, the efficiency of the compression process decreases rapidly. The reason for a low efficiency of compression in the conventional Root's-type device is due to the fact that the inlet charge of fresh gas that is captured in the lobe well or pocket is not compressed until the pocket is exposed to the high pressure discharge region. Upon such exposure to discharge pressure, the low pressure within the pocket becomes pressurized by a .[.block-back.]. .Iadd.blow-back .Iaddend.of gas from the discharge region. This blow-back of gas loads or pressurizes the impeller, causing all the input shaft work on the fresh gas to be done against the discharge pressure level. This is to be contrasted with an efficient isentropic compression process wherein the work is done as the pressure of the fresh gas is built-up gradually from the inlet pressure to the discharge pressure. In this manner, the average pressure against which work must be done is considerably less than that of the discharge.